1. Field of the Invention
Thus, disclosed embodiments relate generally to a power source for sensors. More specifically, the invention relates to an energy harvester that converts mechanical vibration, light, heat (e.g., heat from a body, a combustion device, or other heat-generating thermocouples), radiofrequency, or other forms of energy into electrical energy suitable for use in small, wireless autonomous devices, for example, portable sensors, wearable electronics, motion detectors, wireless sensor networks, sensor-enabled fabrics and other wearable, portable or mobile products.
2. Background of the Invention
Significant interest in vibration energy harvesting has developed over the past decade due to decreasing power demands of electronics and the increasing use of wireless systems. Most vibration energy harvesters consist of a mass attached to a mechanical spring with a transduction mechanism to convert the mechanical energy into electrical energy1, 2, 3. The transduction mechanism is comprised of one or more of the four transducer types: piezoelectric4,5,6, electromagnetic7,8, electrostatic9,10, and more recently magnetostrictive11.
Vibration sources can include: vehicles, such as cars, trains, airplanes, heavy machinery such as tractors or conveyor systems, heavy duty storage containers such as cargo or trash containers or other machines such as computers, power transformers or air conditioners; infrastructure such as bridges, buildings, and ventilation ducts; or multiple forms of human movement3,12. These sources have peak vibration amplitude ranging from 10's of milli g's up to a few g's (where 1 g=9.8 m/s2) at frequencies from less than one Hertz up to a few hundred Hertz12. Human vibration and motion energy is concentrated below 10 Hz, which causes difficulty because lower frequency sources are more difficult to design for due to the requirement of either a highly compliant spring or large mass. This severely limits the applications of vibration energy harvesting from human motion.
Accordingly, it will be desirable to design an apparatus and methods wherein the vibration energy harvesting is compact yet sensitive to low-frequency vibration energy sources. Disclosed embodiments overcome the shortcomings of the prior art as described herein.